The objective of the research is to define the functional interrelationships between those neuronela types which comprise brain stem and spinal networks governing the discharges of preganglionic sympathetic nerves involved in circulatory control. The current proposal is concerned with three aspects of this general problem: 1. Organization of spinal sympathetic circuits. 2. Organization of bulbospinal sympathoinhibitory circuits in baroreceptor reflex arc. 3. Organization of brain stem reticular circuits responsible for rhythmic discharges in sympathetic nerves. The experimental animal will be the cat. Computer techniques (auto- and crosscorrelation; averaging; time interval analysis) will be used to study the relationship between the activity of single brain stem and spinal neurons and that of populations of preganglionic sympathetic nerve fibers contained within cardiovascular pathways.